My answer would depend on how many “names” you expect. If it is a relatively small and constrained list (under a few hundred thousand), I would start with something like:
Create table last_values ( arbitrary_partition text, -- use an app name or something static to define the partition name text, value text, last_upd_ts timestamp, primary key (arbitrary_partition, name); (NOTE: every insert would just overwrite the last value. You only keep the last one.) Then your query is easy: Select name, value, last_upd_ts from last_values where arbitrary_partition = ‘my_app_name’; If the list of names is unbounded/large, then I would be asking, does the query really need every name/value pair? What other way could they grouped together in a reasonable partition? I would use that instead of the arbitrary_partition above and run multiple queries (one for each partition) if a massive list is actually required. I’m assuming that your data arrives in time series order, so that it is easy to just insert the last value into last_values. If you have to read before write, that would be a Cassandra anti-pattern that needs a different solution. (Based on how regular the data points are, I would look at something time-series related with a short TTL.) Sean Durity From: Gábor Auth <auth.ga...@gmail.com> Sent: Tuesday, November 10, 2020 2:39 AM To: user@cassandra.apache.org Subject: [EXTERNAL] Last stored value metadata table Hi, Short story: storing time series of measurements (key(name, timestamp), value). The problem: get the list of the last `value` of every `name`. Is there a Cassandra friendly solution to store the last value of every `name` in a separate metadata table? It will come with a lot of tombstones... any other solution? :) -- Bye, Auth Gábor ________________________________ The information in this Internet Email is confidential and may be legally privileged. It is intended solely for the addressee. Access to this Email by anyone else is unauthorized. If you are not the intended recipient, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it, is prohibited and may be unlawful. When addressed to our clients any opinions or advice contained in this Email are subject to the terms and conditions expressed in any applicable governing The Home Depot terms of business or client engagement letter. The Home Depot disclaims all responsibility and liability for the accuracy and content of this attachment and for any damages or losses arising from any inaccuracies, errors, viruses, e.g., worms, trojan horses, etc., or other items of a destructive nature, which may be contained in this attachment and shall not be liable for direct, indirect, consequential or special damages in connection with this e-mail message or its attachment.
